The present invention relates to large vertical and horizontal shaft machines, and in particular it relates to the lubrication of the thrust bearings used in such machines.
Thrust bearings for large vertical shaft machines usually comprise a downwardly facing ring that is mounted to the rotating component of the machine and a plurality of shoes or bearing segments with upwardly directed bearing surfaces. The bearing shoes support the rotating ring on an oil film which is usually supplied by having the ring and the bearing shoes submerged in an oil bath. The bearing shoes are mounted on a pivot, or by some other means that permits a limited pivoting action, so that the shoe is able to tilt down slightly at the leading edge to form the oil film into a slight wedge-shaped configuration. The tilting action also provides for alignment of the shoe surface with the surface of the rotating ring.
U.S. Pat. No. 3,905,657 issued Sep. 16, 1975 to Isao Ishida et al discloses a thrust bearing shoe that includes an overflow chamber surrounding leading and side circumferencial surfaces of the bearing shoe into which oil is fed to provide an oil film for the sliding surface of the bearing shoe and the rotating ring of the bearing pad. This permits the lubricating oil in the oil bath to be reduced below the level of the rotating ring eliminating agitation of the oil in the oil bath caused by rotation of the bearing rotating ring. However, the bearing shoes rely on their partial immersion in the oil bath and the oil passing from the overflow chamber for cooling. The loads that can be sustained by this thrust bearing are limited by the value of the oil film thickness on the bearing surface, the temperature rise of the lubricant, and the temperature of the bearing shoe. Because the ring and exterior surfaces of the bearing shoe are not immersed in the oil bath, there is a significant reduction in cooling, which becomes more critical at high speed and limits the loads capable of being sustained by the thrust bearings.
U.S. Pat. No. 4,699,524 issued Oct. 13, 1987 to Duncan Bath discloses thrust bearing shoes immersed in the oil bath having a supplementary cooling arrangement to lower and evenly distribute the temperature rise experienced by the bearing shoes. Each of the bearing shoes have at least an upper and a lower portion with a junction between said portions defining a supplementary cooling plane. Passages extend in at least one of the portions for conducting oil through the shoe. The passages have ends terminating at an outer curved end of the shoe. First and second nozzles are attached to each shoe at the end of the passages The nozzles are immersed in the oil bath and oriented to draw oil from the oil bath into the shoe and expel oil from the shoe back into the oil bath in accordance with the movement of oil in the oil bath resulting from the rotating ring agitating the oil. While this bearing shoe has an improved cooling capacity, the bearing losses associated with the drag of the oil bath are present.
Accordingly a need has existed for several years to provide a thrust bearing that has a relatively even and efficient cooling capacity for the thrust bearing so as to control the temperature rise of the coolant on the bearing surface and the temperature of the bearing shoe while at the same time eliminating bearing losses associated with a filled oil bath in which the bearing shoes and the rotating ring are immersed.
The present invention relates to a thrust bearing for use in vertical and horizontal shaft rotating machines. The thrust bearing has a plurality of segmental bearing shoes for use in a non-filled oil collecting chamber that permits oil flow through each bearing shoe, out an leading recessed groove in the bearing shoe and across the bearing shoe upper surface. The bearing shoe of the present invention utilizes cooling passages through the interior of the bearing shoe while maintaining lubrication between the bearing shoe and the rotating ring by flowing oil from a leading edge groove of the bearing shoe. Neither of the rotating ring nor bearing shoes are immersed in an oil bath. Further, the non-filled oil chamber acts more as an oil collection chamber which provides two distinct advantages. One advantage is a reduction in drag losses due to maintaining the level of oil below the machine rotor. Another advantage is one of servicing by the ability to inspect the bearings and all oil conduit connections without being encumbered by an oil level in the chamber covering or partially covering and surrounding the bearing shoes.
In accordance with one aspect of the present invention there is provided a thrust bearing for a rotating machine comprising a non-filled oil chamber, a rotating ring for mounting to a vertical shaft of the rotating machine, and a plurality of segmented bearing shoes. The rotating ring has a first bearing surface. The shoes are mounted in the non-filled oil chamber. Each of the segmented bearing shoes comprises a second surface over which the rotating ring first bearing surface slides. Each bearing shoe has a leading edge and a trailing edge in a direction of shaft rotation. The shoe has an oil inlet located adjacent one of the leading edge and the trailing edge and oil filled passages extending within the bearing shoe from the oil inlet towards the leading edge of the shoe. The shoe further has a recessed groove extending across the bearing shoe adjacent the leading edge in fluid communication with the passages for directing oil from the passages along the groove towards the rotating ring whereby oil passes in the oil inlet, along the passages to regulate bearing shoe temperature and out the groove to spread a lubricating oil film to the leading edge of the bearing segments and between the first and second bearing surfaces.
It is also within the realm of the present invention for the thrust bearing to include an oil reservoir located below the non-filled oil chamber into which oil drains from the non-filled oil chamber and an oil cooling and circulating system comprising a pump, heat exchanger and conduit connectors connected to each oil inlet for circulating oil drained into the oil reservoir through the heat exchanger into the conduit and back into the bearing shoes.
It is also within the realm of the present invention for the thrust bearing shoe to include a secondary oil inlet adjacent the other of the leading edge and trailing edge of the bearing shoe. The secondary oil inlet is in fluid communication with the oil filled passages and the recessed groove for providing a safety back-up lubrication and cooling supply.
Further, due to the non-filled aspect of the oil chamber, an oil supply manifold is included in the chamber that supplies oil to the bearing shoes.